1. Field of the Invention
The present invention relates to a suspension controller for a vehicle, particularly to a suspension controller which is effective against a single shock caused by a bump or dip in a road surface on which an automobile is running.
2. Background Art
Conventionally, the spring constant, damping force, bush characteristic or stabilizer characteristic of each of various suspension components provided between a body of a vehicle and its wheels is altered under control depending on conditions of a road surface or running conditions of the vehicle. This is to prevent the vehicle from being shocked or vibrated and to maintain control and the stability of the vehicle. This can be accomplished, for example, by altering the spring constant of an air spring of a suspension depending on conditions of the road surface, by altering the damping force of a shock absorber, or by simply making the characteristic of a bush or a stabilizer variable. This approach was proposed in the published unexamined Japanese patent applications Nos. Sho-59-23712 and Sho-59-26638. In such control, when a vehicle height sensor detects that the vehicle is running on a rough road or when a brake sensor or an accelerator sensor detects that the front of the vehicle has gone up or down, the characteristic of each suspension of the vehicle is altered to maintain good control and stability of the vehicle running on the rough road, or to prevent the front of the vehicle from going up or down further. However, under the above-mentioned conventional control, the vehicle is not determined to be running on a rough road until a large turbulence is continuously detected by the vehicle height sensor. When the vehicle is judged to be running on a rough road, the spring constants of the suspensions for all the wheels are increased to produce the desired effect. If the vehicle passes over a joint of road patches or a single bump or dip, the vehicle usually receives only one shock and then resumes running on a flat part of the road again, so that the characteristic of each suspension is not altered. For this reason, the passengers of the vehicle are not protected from unpleasant shock due to such single bump or dip. This is different from the case where the vehicle is running on a rough road having continuous bumps or dips.